TY  - JOUR
A1  - Beye, Martin
A1  - Anniyev, Toyli
A1  - Coffee, Ryan
A1  - Dell'Angela, Martina
A1  - Föhlisch, Alexander
A1  - Gladh, J.
A1  - Katayama, T.
A1  - Kaya, S.
A1  - Krupin, O.
A1  - Mogelhoj, A.
A1  - Nilsson, A.
A1  - Nordlund, D.
A1  - Norskov, J. K.
A1  - Oberg, H.
A1  - Ogasawara, H.
A1  - Pettersson, Lars G. M.
A1  - Schlotter, W. F.
A1  - Sellberg, J. A.
A1  - Sorgenfrei, Florian
A1  - Turner, J. J.
A1  - Wolf, M.
A1  - Wurth, Wilfried
A1  - Ostrom, H.
T1  - Selective ultrafast probing of transient hot chemisorbed and precursor States of CO on Ru(0001)
JF  - Physical review letters
N2  - We have studied the femtosecond dynamics following optical laser excitation of CO adsorbed on a Ru surface by monitoring changes in the occupied and unoccupied electronic structure using ultrafast soft x-ray absorption and emission. We recently reported [M. Dell'Angela et al. Science 339, 1302 (2013)] a phonon-mediated transition into a weakly adsorbed precursor state occurring on a time scale of >2 ps prior to desorption. Here we focus on processes within the first picosecond after laser excitation and show that the metal-adsorbate coordination is initially increased due to hot-electron-driven vibrational excitations. This process is faster than, but occurs in parallel with, the transition into the precursor state. With resonant x-ray emission spectroscopy, we probe each of these states selectively and determine the respective transient populations depending on optical laser fluence. Ab initio molecular dynamics simulations of CO adsorbed on Ru(0001) were performed at 1500 and 3000 K providing insight into the desorption process.
Y1  - 2013
U6  - https://doi.org/10.1103/PhysRevLett.110.186101
SN  - 0031-9007
VL  - 110
IS  - 18
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Dell'Angela, M.
A1  - Anniyev, Toyli
A1  - Beye, Martin
A1  - Coffee, Ryan
A1  - Föhlisch, Alexander
A1  - Gladh, J.
A1  - Katayama, T.
A1  - Kaya, S.
A1  - Krupin, O.
A1  - LaRue, J.
A1  - Mogelhoj, A.
A1  - Nordlund, D.
A1  - Norskov, J. K.
A1  - Oberg, H.
A1  - Ogasawara, H.
A1  - Ostrom, H.
A1  - Pettersson, Lars G. M.
A1  - Schlotter, W. F.
A1  - Sellberg, J. A.
A1  - Sorgenfrei, Florian
A1  - Turner, J. J.
A1  - Wolf, M.
A1  - Wurth, W.
A1  - Nilsson, A.
T1  - Real-time observation of surface bond breaking with an X-ray Laser
JF  - Science
N2  - We used the Linac Coherent Light Source free-electron x-ray laser to probe the electronic structure of CO molecules as their chemisorption state on Ru(0001) changes upon exciting the substrate by using a femtosecond optical laser pulse. We observed electronic structure changes that are consistent with a weakening of the CO interaction with the substrate but without notable desorption. A large fraction of the molecules (30%) was trapped in a transient precursor state that would precede desorption. We calculated the free energy of the molecule as a function of the desorption reaction coordinate using density functional theory, including van der Waals interactions. Two distinct adsorption wells-chemisorbed and precursor state separated by an entropy barrier-explain the anomalously high prefactors often observed in desorption of molecules from metals.
Y1  - 2013
U6  - https://doi.org/10.1126/science.1231711
SN  - 0036-8075
VL  - 339
IS  - 6125
SP  - 1302
EP  - 1305
PB  - American Assoc. for the Advancement of Science
CY  - Washington
ER  - 
TY  - JOUR
A1  - Dell'Angela, Martina
A1  - Anniyev, Toyli
A1  - Beye, Martin
A1  - Coffee, Ryan
A1  - Föhlisch, Alexander
A1  - Gladh, Jörgen
A1  - Kaya, Sarp
A1  - Katayama, Tetsuo
A1  - Krupin, Oleg
A1  - Nilsson, Anders
A1  - Nordlund, Dennis
A1  - Schlotter, William F.
A1  - Sellberg, Jonas A.
A1  - Sorgenfrei, Florian
A1  - Turner, Joshua J.
A1  - ÖstrÖm, Henrik
A1  - Ogasawara, Hirohito
A1  - Wolf, Martin
A1  - Wurth, Wilfried
T1  - Vacuum space charge effects in sub-picosecond soft X-ray photoemission on a molecular adsorbate layer
JF  - Structural dynamics
N2  - Vacuum space charge induced kinetic energy shifts of O 1s and Ru 3d core levels in femtosecond soft X-ray photoemission spectra (PES) have been studied at a free electron laser (FEL) for an oxygen layer on Ru(0001). We fully reproduced the measurements by simulating the in-vacuum expansion of the photoelectrons and demonstrate the space charge contribution of the high-order harmonics in the FEL beam. Employing the same analysis for 400 nm pump-X-ray probe PES, we can disentangle the delay dependent Ru 3d energy shifts into effects induced by space charge and by lattice heating from the femtosecond pump pulse. (C) 2015 Author(s).
Y1  - 2015
U6  - https://doi.org/10.1063/1.4914892
SN  - 2329-7778
VL  - 2
IS  - 2
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Katayama, T.
A1  - Anniyev, Toyli
A1  - Beye, Martin
A1  - Coffee, Ryan
A1  - Dell'Angela, M.
A1  - Föhlisch, Alexander
A1  - Gladh, J.
A1  - Kaya, S.
A1  - Krupin, O.
A1  - Nilsson, A.
A1  - Nordlund, D.
A1  - Schlotter, W. F.
A1  - Sellberg, J. A.
A1  - Sorgenfrei, Florian
A1  - Turner, J. J.
A1  - Wurth, W.
A1  - Öström, H.
A1  - Ogasawara, H.
T1  - Ultrafast soft X-ray emission spectroscopy of surface adsorbates using an X-ray free electron laser
JF  - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy
N2  - We report on an experimental system designed to probe chemical reactions on solid surfaces on a sub-picosecond timescale using soft X-ray emission spectroscopy at the Linac Coherent Light Source (LCLS) free electron laser (FEL) at the SLAC National Accelerator Laboratory. We analyzed the O 1s X-ray emission spectra recorded from atomic oxygen adsorbed on a Ru(0001) surface at a synchrotron beamline (SSRL, BL13-2) and an FEL beamline (LCLS, SXR). We have demonstrated conditions that provide negligible amount of FEL induced damage of the sample. In addition we show that the setup is capable of tracking the temporal evolution of electronic structure during a surface reaction of submonolayer quantities of CO molecules desorbing from the surface.
KW  - X-ray emission spectroscopy
KW  - Surface science
KW  - Free electron laser
KW  - Ultrafast
Y1  - 2013
U6  - https://doi.org/10.1016/j.elspec.2013.03.006
SN  - 0368-2048
VL  - 187
IS  - 1
SP  - 9
EP  - 14
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Oberg, H.
A1  - Gladh, Jörgen
A1  - Anniyev, Toyli
A1  - Beye, Martin
A1  - Coffee, Ryan
A1  - Föhlisch, Alexander
A1  - Katayama, T.
A1  - Kaya, Sarp
A1  - LaRue, Jerry
A1  - Mogelhoj, Andreas
A1  - Nordlund, Dennis
A1  - Ogasawara, Hirohito
A1  - Schlotter, William F.
A1  - Sellberg, Jonas A.
A1  - Sorgenfrei, Florian
A1  - Turner, Joshua J.
A1  - Wolf, Martin
A1  - Wurth, W.
A1  - Ostrom, Henrik
A1  - Nilsson, Anders
A1  - Norskov, Jens K.
A1  - Pettersson, Lars G. M.
T1  - Optical laser-induced CO desorption from Ru(0001) monitored with a free-electron X-ray laser: DFT prediction and X-ray confirmation of a precursor state
JF  - Surface science
N2  - We present density functional theory modeling of time-resolved optical pump/X-ray spectroscopic probe data of CO desorption from Ru(0001). The BEEF van der Waals functional predicts a weakly bound state as a precursor to desorption. The optical pump leads to a near-instantaneous (<100 fs) increase of the electronic temperature to nearly 7000 K. The temperature evolution and energy transfer between electrons, substrate phonons and adsorbate is described by the two-temperature model and found to equilibrate on a timescale of a few picoseconds to an elevated local temperature of similar to 2000K. Estimating the free energy based on the computed potential of mean force along the desorption path, we find an entropic barrier to desorption (and by time-reversal also to adsorption). This entropic barrier separates the chemisorbed and precursor states, and becomes significant at the elevated temperature of the experiment (similar to 1.4 eV at 2000 K). Experimental pump-probe X-ray absorption/X-ray emission spectroscopy indicates population of a precursor state to desorption upon laser-excitation of the system (Dell'Angela et al., 2013). Computing spectra along the desorption path confirms the picture of a weakly bound transient state arising from ultrafast heating of the metal substrate. (C) 2015 Elsevier B.V. All rights reserved.
KW  - CO desorption
KW  - Potential of mean force
KW  - Two-temperature model
KW  - Pump-probe
KW  - X-ray spectroscopy
KW  - Density functional theory
Y1  - 2015
U6  - https://doi.org/10.1016/j.susc.2015.03.011
SN  - 0039-6028
SN  - 1879-2758
VL  - 640
SP  - 80
EP  - 88
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Wolf, Thomas J. A.
A1  - Holzmeier, Fabian
A1  - Wagner, Isabella
A1  - Berrah, Nora
A1  - Bostedt, Christoph
A1  - Bozek, John
A1  - Bucksbaum, Phil
A1  - Coffee, Ryan
A1  - Cryan, James
A1  - Farrell, Joe
A1  - Feifel, Raimund
A1  - Martinez, Todd J.
A1  - McFarland, Brian
A1  - Mucke, Melanie
A1  - Nandi, Saikat
A1  - Tarantelli, Francesco
A1  - Fischer, Ingo
A1  - Gühr, Markus
T1  - Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra
JF  - Applied sciences
N2  - Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymines neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependent dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes.
KW  - ultrafast dynamics
KW  - Auger electron spectroscopy
KW  - photofragmentation
KW  - photochemistry
Y1  - 2017
U6  - https://doi.org/10.3390/app7070681
SN  - 2076-3417
VL  - 7
IS  - 7
PB  - MDPI
CY  - Basel
ER  - 
TY  - JOUR
A1  - Wolf, Thomas J. A.
A1  - Holzmeier, Fabian
A1  - Wagner, Isabella
A1  - Berrah, Nora
A1  - Bostedt, Christoph
A1  - Bozek, John
A1  - Bucksbaum, Philip H.
A1  - Coffee, Ryan
A1  - Cryan, James
A1  - Farrell, Joe
A1  - Feifel, Raimund
A1  - Martinez, Todd J.
A1  - McFarland, Brian
A1  - Mucke, Melanie
A1  - Nandi, Saikat
A1  - Tarantelli, Francesco
A1  - Fischer, Ingo
A1  - Gühr, Markus
T1  - Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra
JF  - Applied Sciences
N2  - Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymine′s neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependent dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes.
KW  - ultrafast dynamics
KW  - Auger electron spectroscopy
KW  - photofragmentation
KW  - photochemistry
Y1  - 2017
U6  - https://doi.org/10.3390/app7070681
SN  - 2076-3417
VL  - 7
IS  - 7
PB  - MDPI
CY  - Basel
ER  - 
TY  - GEN
A1  - Wolf, Thomas J. A.
A1  - Holzmeier, Fabian
A1  - Wagner, Isabella
A1  - Berrah, Nora
A1  - Bostedt, Christoph
A1  - Bozek, John
A1  - Bucksbaum, Philip H.
A1  - Coffee, Ryan
A1  - Cryan, James
A1  - Farrell, Joe
A1  - Feifel, Raimund
A1  - Martinez, Todd J.
A1  - McFarland, Brian
A1  - Mucke, Melanie
A1  - Nandi, Saikat
A1  - Tarantelli, Francesco
A1  - Fischer, Ingo
A1  - Gühr, Markus
T1  - Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra
N2  - Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymine′s neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependent dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 386 
KW  - Auger electron spectroscopy
KW  - photochemistry
KW  - photofragmentation
KW  - ultrafast dynamics
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-402692
ER  - 
TY  - JOUR
A1  - Yang, Jie
A1  - Guehr, Markus
A1  - Shen, Xiaozhe
A1  - Li, Renkai
A1  - Vecchione, Theodore
A1  - Coffee, Ryan
A1  - Corbett, Jeff
A1  - Fry, Alan
A1  - Hartmann, Nick
A1  - Hast, Carsten
A1  - Hegazy, Kareem
A1  - Jobe, Keith
A1  - Makasyuk, Igor
A1  - Robinson, Joseph
A1  - Robinson, Matthew Scott
A1  - Vetter, Sharon
A1  - Weathersby, Stephen
A1  - Yoneda, Charles
A1  - Wang, Xijie
A1  - Centurion, Martin
T1  - Diffractive Imaging of Coherent Nuclear Motion in Isolated Molecules
JF  - Physical review letters
N2  - Observing the motion of the nuclear wave packets during a molecular reaction, in both space and time, is crucial for understanding and controlling the outcome of photoinduced chemical reactions. We have imaged the motion of a vibrational wave packet in isolated iodine molecules using ultrafast electron diffraction with relativistic electrons. The time-varying interatomic distance was measured with a precision 0.07 angstrom and temporal resolution of 230 fs full width at half maximum. The method is not only sensitive to the position but also the shape of the nuclear wave packet.
Y1  - 2016
U6  - https://doi.org/10.1103/PhysRevLett.117.153002
SN  - 0031-9007
SN  - 1079-7114
VL  - 117
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - GEN
A1  - Yang, Jie
A1  - Guehr, Markus
A1  - Vecchione, Theodore
A1  - Robinson, Matthew Scott
A1  - Li, Renkai
A1  - Hartmann, Nick
A1  - Shen, Xiaozhe
A1  - Coffee, Ryan
A1  - Corbett, Jeff
A1  - Fry, Alan
A1  - Gaffney, Kelly
A1  - Gorkhover, Tais
A1  - Hast, Carsten
A1  - Jobe, Keith
A1  - Makasyuk, Igor
A1  - Reid, Alexander
A1  - Robinson, Joseph
A1  - Vetter, Sharon
A1  - Wang, Fenglin
A1  - Weathersby, Stephen
A1  - Yoneda, Charles
A1  - Wang, Xijie
A1  - Centurion, Martin
T1  - Femtosecond gas phase electron diffraction with MeV electrons
N2  - We present results on ultrafast gas electron diffraction (UGED) experiments with femtosecond resolution using the MeV electron gun at SLAC National Accelerator Laboratory. UGED is a promising method to investigate molecular dynamics in the gas phase because electron pulses can probe the structure with a high spatial resolution. Until recently, however, it was not possible for UGED to reach the relevant timescale for the motion of the nuclei during a molecular reaction. Using MeV electron pulses has allowed us to overcome the main challenges in reaching femtosecond resolution, namely delivering short electron pulses on a gas target, overcoming the effect of velocity mismatch between pump laser pulses and the probe electron pulses, and maintaining a low timing jitter. At electron kinetic energies above 3 MeV, the velocity mismatch between laser and electron pulses becomes negligible. The relativistic electrons are also less susceptible to temporal broadening due to the Coulomb force. One of the challenges of diffraction with relativistic electrons is that the small de Broglie wavelength results in very small diffraction angles. In this paper we describe the new setup and its characterization, including capturing static diffraction patterns of molecules in the gas phase, finding time-zero with sub-picosecond accuracy and first time-resolved diffraction experiments. The new device can achieve a temporal resolution of 100 fs root-mean-square, and sub-angstrom spatial resolution. The collimation of the beam is sufficient to measure the diffraction pattern, and the transverse coherence is on the order of 2 nm. Currently, the temporal resolution is limited both by the pulse duration of the electron pulse on target and by the timing jitter, while the spatial resolution is limited by the average electron beam current and the signal-to-noise ratio of the detection system. We also discuss plans for improving both the temporal resolution and the spatial resolution.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 326 
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-394989
ER  -